Horrible framerate <i>and</i> it forgets anything that happened more than 0.9 seconds in the past. And they needed the actual, fully implemented game before they could begin to train it. So just, cut out the middleman, and play the game directly.
From the gaming point of view it would be much better to integrate the original engine's scene output with partial or complete AI rendering, training the AI to produce hyper realistic graphics.
Flash back to playing the Ziggurat Vertigo level with 25 reaper bots, squatting on the roof of one of the areas and just seeing random gibs arcing up around me.